Typically, turbine airfoils usable in turbine engines include a plurality of internal cooling passages. These cooling passages are typically formed with a ceramic core. Ceramic cores are often formed with molding systems, such as those typically used in the plastics injection molding industry; however, for turbine parts more wear-resistant metal alloys are needed for the molding systems to withstand the abrasive ceramic slurries that are typically used to form the ceramic cores. The molding systems typically comprise mold plates and a cavity space within the mold plates. The mold cavity space defines the ceramic core shape, dimensions and features, including the complex cooling passages common to turbine airfoils.
Two general methods exist for making the mold cavities. The first method involves creating the cavity space by removing material from the mold plates. Because the mold plates are made from wear-resistant metal alloys, conventional machining of these plates is extremely difficult, expensive, time consuming, and is also limited to machining simple mold cavity geometries. Typically, non-conventional metal removing methods, such as electrical discharge machining (EDM) or chemical etching are needed to create the cavity space that forms the ceramic core.
The second method of creating the mold cavity shape involves the use of a metal insert that has an internal cavity shape. This metal insert is placed into a space machined into the mold plates. The approach allows the use of lower cost and easier to machine metals for the mold plates and limits the use of wear-resistant metal alloys to the metal inserts. However, as with the first method, this approach requires non-conventional, expensive and time consuming metal removal methods to create the cavity shape within the metal insert.
These two conventional methods of creating a ceramic core molding system typically take about sixteen to twenty weeks to complete. In an attempt to reduce lead-time and allow for design changes, less wear resistant and easier to machine alloys have been used as metal inserts. However, these materials have a very limited life due to their lower wear resistance and need to be replaced often, which adds extra cost to the ceramic core making process. Once the design changes are completed, an additional four to six weeks are needed to make the insert from a wear-resistant metal alloy. Therefore, a need exists for a more time efficient and lower cost process of producing a ceramic core usable in the production of a turbine airfoil.